Theresa May has been urged to apologise for Britain’s historical legacy of anti-gay laws across the Commonwealth as leaders of the 53 member states gather for a summit in London on Monday.

Gay rights campaigner Peter Tatchell argued that the government should help address colonial-era legislation that treats more than 100 million lesbian, gay, bisexual and trans people across the Commonwealth as criminals.

The Guardian understands that the government plans to make an announcement on the issue at the heads of government summit later this week – but will avoid any grand political gestures that might prompt accusations of neocolonial lecturing.

We won in Trinidad. Now it’s time to end all homophobic laws in the Commonwealth

Tatchell, a veteran campaigner, said: “I urge Theresa May to acknowledge and apologise for what Britain did by forcing homophobic laws on colonial peoples. These laws remain today and are menacing the lives of millions of LGBT people in Commonwealth countries.

“An apology would wrong-foot homophobes in the anti-gay member states by highlighting the nonindigenous nature of their current homophobic legislation.”

He added: “The humility and remorse of an apology would be far more powerful and effective than neocolonial lecturing and denunciation of homophobia by the UK government.”

Same-sex relations are still illegal in 36 Commonwealth member states, including nine that have a maximum penalty of life imprisonment.

Labour peer and gay rights campaigner Waheed Alli said the summit, the first in the UK since 1997, presented a “unique” opportunity for the government to ensure that LGBT rights was a key part of the agenda.

Lord Alli said: “I would urge the prime minister to recognise the special responsibility the UK has to be part of decriminalising homosexuality across the Commonwealth, given our historic role in imposing these laws on other countries in the first place.

“It is vital that ministers make the most of this opportunity to speak to other leaders and support LGBT civil society groups working on the ground in often dangerous situations.”

He suggested that decriminalising homosexuality should be a basic principle of UK foreign policy, with ministers developing a clear plan for each country based on lobbying government, boosting grassroots efforts and supporting legal action.

Tory MP Nick Herbert, chair of the all-party group on global LGBT rights, added: “These are countries which have flagrantly breached the Commonwealth charter by their treatment of LGBT people, and both the government and the Commonwealth itself should call them out on it.

“The FCO [Foreign and Commonwealth Office] has been doing a lot of good work, and the prime minister has taken a stronger stand than ever before. What we should avoid is raising the issue in a way which backfires.”

The group, which is supported by 100 MPs and peers across the political parties, published a major report in 2016 that highlighted the need for ministers to do more to tackle serious human rights abuses suffered by LGBT people across the globe.

Paul Dillane, director of the Kaleidoscope Trust, said: “The summit is a test for the UK as to how it sensitively approaches the issue of international LGBT rights, particularly given our colonial past.”

This year’s summit will officially host gay rights activists under the umbrella of the Commonwealth Equality Network, giving grassroots campaigners the opportunity to lobby international government ministers and officials directly.

A Downing Street spokeswoman said: “This is an important issue and one many people across our country rightly feel strongly about.

“As the prime minister has said, we have a special responsibility to help change hearts and minds, and we will ensure that these important issues are discussed during the Commonwealth summit week.”

Last week, British diver Tom Daley made a plea for Commonwealth countries to decriminalise homosexuality after winning a gold medal at the Commonwealth Games in Australia. The athlete tweeted:

Tom Daley (@TomDaley1994)

🥇G O L D 🥇•••🏳️‍🌈 37 of the competing nations criminalise being LGBT+. I feel so lucky to be able to be openly who I am without worry. I hope one day every athlete from every nation in the commonwealth will be free to compete openly as who they are too! 🏳️‍🌈 pic.twitter.com/ry4GPiZhdB

The next Commonwealth summit, in two years’ time, was widely expected to be held in Malaysia. However, it has been suggested that the south-east Asian country’s gay rights record, among other issues, could mean it is hosted elsewhere.

Last week, a court judgment in Trinidad and Tobago raised hopes that gay sex between consenting men could soon be decriminalised, and campaigners said similar decisions might follow elsewhere in the Caribbean.

However, in other countries, such as Nigeria and Uganda, the situation is getting worse.